In recent years, the use of remote keyless entry (RKE) systems for automotive and security applications have increased significantly. The conventional remote keyless entry (RKE) system consists of a RKE transmitter and a base station. The RKE transmitter has activation buttons. When an activation button is pressed, the RKE transmitter transmits a corresponding radio frequency data to the base station. The base station receives the data and performs appropriate actions such as unlock/lock car doors or trunks if the received data is valid. In the conventional RKE systems, the data is transmitted from the RKE transmitter to the base station, but not from the base station to the transmitter. This is often called unidirectional communication.
Much more sophisticated RKE systems can be made by using a bidirectional communication method. The bidirectional remote keyless entry system consists of a transponder and a base station. The transponder and base station can communicate by themselves without human interface buttons. The base station sends a command to the transponder and the transponder can respond to the base station accordingly if the command is valid. By utilizing the bidirectional communication method, one can unlock/lock his/her car doors or trunks remotely without pressing any buttons. Therefore, a fully hands-free access to the room or car is now possible.
The bidirectional communication RKE system consists of base station and transponder. The base station can send and receive low frequency command/data, and also can receive VHF/UHF/Microwave signals. The transponder can detect the low frequency (LF) data and transmit data to the base station via low frequency or VHF/UHF/Microwave. In applications, the bidirectional transponder may have the activation buttons as optional, but can be used without any activation button, for example, to unlock/lock car doors, trunks, etc.
For a reliable hands-free operation of the transponder that can operate without human interface, the transponder must be intelligent enough on decision making for detecting input signals correctly and managing its operating power properly for longer battery life. The idea in this application describes the dynamic configuration of the transponder, that can reconfigure the transponder's feature sets any time during applications, to communicate with the base station intelligently by itself in the hand-free operation environment.
Referring to FIG. 1, depicted is a prior art passive remote keyless entry (RKE) system. These wireless RKE systems typically are comprised of a base station 102, which is normally placed in the vehicle in automobile applications, or in the home or office in security entrance applications, and one or more RKE transponders 104, e.g., key-fobs, that communicate with the base station 102. The base station 102 may comprise a radio frequency receiver 106, antenna 110 and, optionally, a low frequency transmitter/reader 108 and associated antenna 112. The transponder 104 may comprise a radio frequency transmitter 122, an encoder 124 coupled to the transmitter 122, antenna 118 and, optionally, a low frequency transponder 126 and associated antenna 120. The transmitter 122 may communicate with the receiver 106 by using very high frequency (VHF) or ultra high frequency (UHF) radio signals 114 at distances up to about 100 meters so as to locate a vehicle (not shown) containing the base station 102, locking and locking doors of the vehicle, setting an alarm in the vehicle, etc. The encoder 124 may be used to encrypt the desired action for only the intended vehicle. Optionally, the low frequency transponder 126 may be used for hands-free locking and unlocking doors of a vehicle or building at close range, e.g., 1.5 meters or less over a magnetic field 116 that couples between the coils 112 and 120.
The RKE transponder 104 is typically housed in a small, easily carried key-fob (not shown) and the like. A very small internal battery is used to power the electronic circuits of the RKE transponder when in use. The duty cycle of the RKE transponder must, by necessity, be very low otherwise the small internal battery would be quickly drained. Therefore to conserve battery life, the RKE transponder 104 spends most of the time in a “sleep mode,” only being awakened when a sufficiently strong magnetic field interrogation signal is detected. The RKE transponder will awaken when in a strong enough magnetic field at the expected operating frequency, and will respond only after being thus awakened and receiving a correct security code from the base station interrogator, or if a manually initiated “unlock” signal is requested by the user (e.g., unlock push button on key-fob).
This type of RKE system is prone to false wake-up, short battery life, unreliable operating range that is too dependant upon orientation of the key fob (not shown). Thus, it is necessary that the number of false “wake-ups” of the RKE transponder circuits be keep to a minimum. This is accomplished by using low frequency time varying magnetic fields to limit the interrogation range of the base station to the RKE transponder. The flux density of the magnetic field is known as “field intensity” and is what the magnetic sensor senses. The field intensity decreases as the cube of the distance from the source, i.e., 1/d3. Therefore, the effective interrogation range of the magnetic field drops off quickly. Thus, walking through a shopping mall parking lot will not cause a RKE transponder to be constantly awakened. The RKE transponder will thereby be awakened only when within close proximity to the correct vehicle. The proximity distance necessary to wake up the RKE transponder is called the “read range.” The VHF or UHF response transmission from the RKE transponder to the base station interrogator is effective at a much greater distance and at a lower transmission power level.
When magnetic flux lines cut a coil of wire, an electric current is generated, i.e., see Maxwell's Equations for current flow in an electric conductor being cut by a magnetic field flux. Therefore the detected magnetic flux density will be proportional to the amount of current flowing in the pick-up coil.
In a closely coupled or near field noisy environment, however, a noise source, e.g., magnetic or electromagnetic, could cause the analog front-end and associated external control device to “wake-up” or remain “awake” and thus cause increased power consumption and thereby reduce battery life. An effective way of conserving battery power is to turn off, e.g., disconnect or put into a “sleep mode” the electronic circuits of the RKE device and any associated circuitry not required in detecting the presence of an electromagnetic RF signal (interrogation challenge) from the keyless entry system reader. Only when the interrogation signal is detected, are the electronic circuits of the RKE device reconnected to the battery power source (wake-up). A problem exists, however, when the transponder receiver is exposed to noise sources such as electromagnetic radiation (EMR) emanating from, for example, televisions and computer monitors having substantially the same frequency as the interrogation signal, the RKE device will wake-up unnecessarily. If the RKE transponder receiver is exposed to a continuous noise source, the battery may be depleted within a few days.
Therefore, there is a need for preventing or substantially reducing false “wake-up” of the RKE transponder.